ASwiftTour(4)-ObjectsandClasses

2019-11-14 20:25:23

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Objects and Classes(對象和類)

用 class 關鍵字后面跟一個類名來創建一個class，在一個類中聲明常亮或變量，他存在于當前類的上下文，函數的方法是同樣的

var numberOfSides = 0    let numberOfSidesLet = 1        func simpleDescription() -> String    {        return "A shape with /(numberOfSides)  /(numberOfSidesLet) sides."    }

通過括號的方式來創建一個類實例，使用點語法來訪問該實例的屬性和方法

var shape = Shape()shape.numberOfSides=10var str = shape.simpleDescription()PRintln(str)

吐槽一下，不知道是xcode6 bate版本問題還是什么原因，寫代碼的提示功能特別差

這個版本的一個重要的修改：在創建的時候設置初始值的項，使用init來創建，如下：

 1 class Shape { 2      3     var name:String 4      5     init(name:String) 6     { 7         self.name = name 8     } 9     10     var numberOfSides = 011     let numberOfSidesLet = 112     13     14     func simpleDescription() -> String15     {16         return "A shape with /(numberOfSides)  /(numberOfSidesLet) sides."17     }18 }

請注意 self 關鍵字用來區分屬性name 和參數 name(這個和oc中的還是一樣)

如果你要釋放一些對象，那么需要創建一個deinitializer，使用deinit來釋放資源

子類和父類之間用冒號分開，在繼承標準的子類時，不需要聲明，所以可以根據需要來忽略或者包括父類

子類重寫父類的方法要使用overside關鍵字(C#,java比較相似)，如果沒有重載，則會提示錯誤

class Square: Shape {       var sideLength: Double        init(sideLength:Double,name:String)    {        self.sideLength = sideLength        super.init(name:name)        numberOfSides = 4    }        func area() -> Double    {        return sideLength * sideLength    }        override func simpleDescription() -> String    {        return "A square with sides of length /(sideLength)"    }} var square = Square(sideLength:10.1,name:"my test") square.area() var str = square.simpleDescription() println(str)

除了簡單的屬性，屬性也可以有getter 和 setter方法

 1 class EquilateralTriangle: Shape { 2     3     var sideLength:Double = 0.0 4      5     init(sideLength:Double,name:String) 6     { 7         self.sideLength = sideLength 8         super.init(name:name) 9         numberOfSides=310     }11     12     var perimeter:Double13     {14         get{15             return 3.0*sideLength16         }17         set18         {19             sideLength = newValue/3.020         }21     }22     23     override func simpleDescription()->String24     {25         return "An equilateral triagle with sides of length /(sideLength)"26     }27 }28  var triangle = EquilateralTriangle(sideLength:3.1,name:"a triangle")29  println(triangle.perimeter)30  triangle.perimeter = 9.931  println(triangle.sideLength)

在perimeter的setter方法中，新值得隱式名稱是newValue,你可以在setter之后提供一個名字

初始化EquilateralTriangle類有三步：

1. 設置屬性的值

2. 調用父類的構造方法(init)

3. 改變父類定義的屬性值，其他的方法也可以在這里設置

如果你不需要計算屬性，但是在setter之前或者之后執行，可以使用willSet和didSet，例如：下面的類永遠保證三角形的邊長等于正方形的邊長

class TriangleAndSquare {       var triangle:EquilateralTriangle    {    willSet    {        square.sideLength = newValue.sideLength    }    }        var square:Square    {     willSet     {        triangle.sideLength = newValue.sideLength    }    }        init(size:Double,name:String)    {        square = Square(sideLength:size,name:name)        triangle = EquilateralTriangle(sideLength:size,name:name)    }}        var triangleAndSquare = TriangleAndSquare(size:10,name:"ray test shape")        println(triangleAndSquare.square.sideLength)        println(triangleAndSquare.triangle.sideLength)        triangleAndSquare.square = Square(sideLength:50,name:"larger square")        println(triangleAndSquare.triangle.sideLength)        println(triangleAndSquare.square.sideLength)//打印出來的值為：10.0，10.0，50.0，50.0

函數和方法有一個不同點，函數的參數名只能在函數中使用，but parameters names in methods are also used when you call the method (except for the first parameter). By default, a method has the same name for its parameters when you call it and within the method itself. You can specify a second name, which is used inside the method(這個不知道怎么翻譯)

 1 class Counter { 2     3     var count:Int = 0 4     func incrementBy(amount:Int,numberOfTimes times:Int) 5     { 6         count += amount*times 7     } 8 } 9  var counter = Counter()10  counter.incrementBy(2,numberOfTimes:7)11

當使用可選值時，可以像方法屬性一樣在操作符前使用問號(?)，如果值本來就是nil，那所有在？之后的代碼將會忽略，整個表達式都是nil，Otherwise, the optional value is unwrapped, and everything after the ? acts on the unwrapped value. In both cases, the value of the whole expression is an optional value.

1  let optionalSquare :Square?=Square(sideLength:2.5,name:"optional square")2  let sideLength = optionalSquare?.sideLength  //注意：等號和optionalSquare之間必須有空格，不知道編譯器為什么會這樣